Try using this code in the onclick instead. It has been updated to work with the latest version of eCart:
if ($('#Payment_Standout_Default').h5Validate('allValid')) this.style.display='none';
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.